website: Generalized advice on modules with provider configs
website: Generalized advice on modules with provider configs

As part of documenting the new module for_each capabilities we added a
section noting that shared modules using the legacy pattern of declaring
their own provider configurations would not be compatible with them.

However, that also applies to the new module depends_on and several folks
participating in the beta pointed out that the documentation wasn't
discussing that at all.

In order to generalize the advice, I've moved the old content we had
(since v0.11) recommending against provider configurations in shared
modules out into its own section, now being more explicit that it is
a legacy pattern and not recommended, and then folded the content about
for_each and count, now also including depends_on, into that expanded
section.

As is often the case, that had some knock-on effects on the content on
the rest of this page, so there's some general editing and reorganization
here. In particular, I moved the "Multiple Instances of a Module" section
much further up the page because it's content relevant to users of
shared modules, while the later content on this page is more aimed at
authors of shared modules, including the new section about the legacy
pattern.

hashicorp/terraform,apparentlymart/terraform,apparentlymart/terraform,ewbankkit/terraform,tommynsong/terraform,tommynsong/terraform,apparentlymart/terraform,rnaveiras/terraform,pdecat/terraform,apparentlymart/terraform,ewbankkit/terraform,hashicorp/terraform,rnaveiras/terraform,tommynsong/terraform,pdecat/terraform,apparentlymart/terraform,hashicorp/terraform,ewbankkit/terraform,pdecat/terraform,ewbankkit/terraform,rnaveiras/terraform,pdecat/terraform